The present invention relates to a variable displacement compressor, which supplies refrigerant from a discharge pressure zone to a control pressure chamber and releases the refrigerant from the control pressure chamber to a suction pressure zone, thereby controlling the pressure in the control pressure chamber and controlling the displacement in accordance with the pressure in the control pressure chamber.
When the displacement of this type of variable displacement compressor is small, that is, when the flow rate of refrigerant is low, pulsation caused by self-excited vibration of reed valves reaches pipes outside the compressor, which generates unusual noise. Thus, the compressor disclosed in Japanese Laid-Open Patent Publication No. 2008-115762 has a first control valve in a suction passage that extends from a suction port for introducing refrigerant from the outside to the suction port in the compressor. The valve body of the first control valve is urged in a direction to close the suction passage, and the pressure in the valve chamber, which communicates with the crank chamber as a control pressure chamber and the suction pressure act against each other with the valve body in between. The first control valve adjusts the cross-sectional area of the suction passage in accordance with the pressure in the valve chamber.
When a compressor having such a first control valve is operating at a small displacement, the difference between the refrigerant pressure at the suction port and the refrigerant pressure in the suction chamber is reduced, so that the cross-sectional area of the suction passage is reduced, accordingly. This limits spread of pulsation caused by self-excited vibration of the reed valves to pipes outside the compressor.
However, when the first control valve, which controls the opening/closing state of the supply passage, is in an open state (an OFF state or a state for varying the displacement), the valve chamber and the suction chamber always communicate with each other. In this case, since the pressure in the valve chamber is relatively low, pulsation generated during the variable displacement operation may not be sufficiently limited.